Electric valve circuit



Feb. 20, 1940. E. E. MOYER ELECTRIC VALVE CIRCUIT Original Filed April 17, 1937 3 Sheets-Sheet 1 a. a a a a u a Invent 0Y Fig.2.

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E. E. MOYER ELECTRIC VALVE CIRCUIT Original Filed April 17. 1937 3 Sheets-Sheet 3 Inventor: Elmo E.MO L .JGT,

His Attorney.

Patented Feb. 20, 1940 UNITED STATES ELECTRIC VALVE CIRCUIT Elmo E. Moyer, Scotia, Y., assignor to General Electric Company, a corporation of New York Original application April 17, 1937, Serial No. 137,525. Divided and this application August 11, 1937, Serial No. 158,559

8 Claims.

This application is a division of my copending I patent application Serial No. 137,525, filed April 17, 1937, and assigned to the assignee of the present application.

There has been an ever increasing application of synchronous machines in electric power generating, transmission and distribution systems. coincidentally with this widespread application of synchronous machines, attention has been directed to the problem of increasing the power limits of the machines to improve the stability of the associated electric power systems.

In view of these factors, there has been evidenced a decided need for arrangements to increase the steady state power limits of synchronous machines so that the machines may operate to supply overloads without falling out of synchronism with the associated system. Moreover, it is important that the synchronous machines 4 be capable of assuming the increase in load in practical simultaneity with such increase so that the continuity or service is not disturbed. Furthermore, it has been evidenced that there is need for electric valve apparatus capable of performing this type of control without involving expensive and complicated equipment. However, it is important that the control equipment for the electric valve translating apparatus be susceptible of energizing the field circuit of the synchronous machine to maintain a predetermined terminal voltage thereof, and also be arranged to increase the power limit of the machine.

It is an object of my invention to provide a new and improved electric valve translating system.

It is another object of my invention to provide a new and improved control circuit for electric valve translating apparatus.

In accordance with the illustrated embodiments of my invention, I provide new and improved electric valve control systems for increasing the steady state power limit of dynamo-electric machines of the synchronous type. In particular,-I provide electric valve apparatus for supplying direct current to the armature windings of a dynamo-electric machine to cause said machine to operate higher up on the saturation curve, there by increasing the steady state power limit of the machine. The electric valve apparatus comprises two groups of electric valves for transmitting energy from a polyphase alternating current circuit to a load circuit which, in thisinstance, is the field circuit and armature winding of a dynamo-electric machine of the synchronous type. The groups of electric valves are arranged to operate as a full wave rectifier for a certian range of operation of the machine and hence do not establish a unidirectional magnetization of the armature winding. I provide an excitation circuit including a voltage sensitive circuit for controlling both groups of valves during this range of operation in accordance with the armature voltage of the machine. For values of load transfer above this range, the excitation circuit controls the conductivity of one group of valves to maintain the voltage constant, and controls the conductivity of the other group of valves in accordance with the load current to establish a unidirectional magnetization of the armature current by transmitting to the armature winding a resultant current having a unidirectional component.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims. Fig. l of the accompanying drawings diagrammatically illustrates my invention as applied to a dynamo-electric machine of the synchronous type in which a controlled rectifier supplies current to the armature windings; Figs. 2, 3, 4 and 4a diagrammatically show other embodiments of my invention in which the control of the current transmitted to the armature windings is effected by electric valve means differently arranged.

Fig. 1 of the accompanying drawings diagrammatically illustrates an embodiment of my invention as applied to a dynamo-electric machine I of the synchronous type having armature phase windings 2, 3 and 4 provided with a neutral connection 5, an associated core member or structure. 5' and a relatively movable field winding 6. The armature windings 2, 3 and 4 are connected to an alternating current circuit 1 which may function as either a supply circuit or a load circuit. An exciter is connected to the field winding 6 to supply direct current thereto and includes an armature memer 8 and a field winding 9. A sub-- exciter I0 may be employed to control the energization of the field winding 9 of the main exciter.

An excitation system II is associated with the main exciter and the sub-exciter H! to control the energization of the field winding 6 in accordance with an electrical condition such as the voltage of the alternating current circuit 1 or in accordance with the terminal voltage of the armature windings of the dynamo-electric machine I. While for the purpose of explaining my invention,

I have chosen to represent the excitation circuit as being of the vibratory type, it should be understood that I may employ any other conventional voltage regulating device for controlling the energization of the field winding 6 in accordance with a predetermined electrical condition. The excitation system H may include a voltage responsive coil l2 energized from the alternating current circuit 1 through a transformer I3, a system of vibratory cooperating contacts I4 and an actuating coil I which is responsive to the armature voltage of the sub-exciter I0. It will be understood by those skilled in the art that the actuating coil I2 may be made responsive to polyphase voltage conditions of the alternating current circuit 1 so that the excitation system I I of machine I may be properly -controlled under imbalanced operating conditions. The excitation system serves to intermittently short circuit a resistance I 6 connected in the field circuit of the sub-exciter I Il'to control the voltage thereof in accordance with the voltage of the circuit 1.

To supply direct current to armature windings 2, 3 and 4 of dynamo-electric machine I to cause the machine to operatehigher upon the saturation curve, I provide a plurality of electric valve means I1, I 8 and I9 which are connected between different armature windings and the neutral connection 5 thereof through a smoothing inductive reactance 20. The electric valve means I'I, I8 and I9 are preferably of the type employing an ionizable medium such as a gas or a vapor and each includes an anode 2|, a cathode 22 and a control member 23 for controlling the conductivity of the associated discharge path. Smoothing inductive reactapce 24 may also be connected in series relation with the electric valve means I1, I8 and I9. As an agency for controlling the conductivities of the electric valve means I], I8 and I9 in accordance with a predetermined electrical condition of the alternating current circuit I or in accordance with a predetermined electrical condition of the armature windings 2, 3 and 4 of'machine I, I provide a control circuit 25 which is responsive to the current of the alternating current circuit 1. A suitable inductive device such as a current transformer 26 may be associated with each of the conductors of the circuit I to provide an alternating voltage which varies in accordance with the current, and a circuit 21 is used to provide a unidirectional voltage which varies in accordance with the current of the alternating current circuit 1. The circuit 21 may include a full wave rectifying device 28, an adjustable resistor 29 connected across the terminals of the current transformer 26, an impedance element such as a resistance 30 and a capacitance 3| connected in parallel relation with the resistance 30. It will be understood bythose skilled in the art that the control of the electric valves I'I, I8 and I9 may be made responsive to polyphase conditions of the alternating current circuit 1; for example, the currents in the various conductors of circuit 1 may be summated or integrated by well known arrangements to control the electric valves I1, I8 and I9 in accordance with the polyphase current conditions. To impress on control members 23 of electric valve means I1, I8 and I9 alternating voltages adjustable in phase, I employ a transformer 32 having primary windings 33 and secondary windings 34 which are connected to control members 23 through current limiting resistance 35. Connected in series relation with the resistance 30, I employ a suitable source of negative unidirectional biasing potential such as a battery 36 which introduces in the control circuit 25 a potential which acts in opposition to the voltage provided by the resistance 30 and the associated circuit 21. The magnitude of the potential provided by range of current in the'circuit I, and the circuit 21 may be energized to provide a voltage to render ineffective or neutralize the potential of battery 26 when the current of circuit 1 increases beyond a predetermined value, so that the conductivities of electric valves I], I8 and I9 are controlled to supply a unidirectional component of current to armature .windings 2, 3 and 4 of machine I in accordance with the alternating component of current of the armature windings. Any suitable phase shifting arrangement, as a rotary phase shifting device 31, may be employed to control the phase of the alternating voltage introduced in control circuit 25 by transformer The operation of the embodiment of my invention diagrammatically shown in Fig. 1 will be explained by considering the system when the dynamo-electric machine I is operating as a synchronous generator to supply alternating current to the circuit I. Let it be assumed that the control circuit 25 is adjusted so that the unidirectional biasing potential provided by the battery 36 is sufficiently great to maintain the electric valve means II, I8 and I9 nonconductive within a predetermined range of current transfer between the armature windings 2, 3 and 4 of ma chine I and the alternating current circuit 1. As

the current varies within this range of values, the

excitation system II will respond to control the energization of field winding 6 so that the voltage of the alternating current circuit 1 is maintained at a predetermined value. If it be assumed further that the current supplied by the machine I increases to a value above said predetermined range of values, the voltage appearing across the terminals of resistance 30 will become sufficiently large so that the resultant unidirectional voltage acting in the control circuit 25 is reduced to render electric valves II, I8 and I9 conductive at a predetermined time during the respective positive half cycles of anode voltage to produce unidirectional components of current in the arma-' comes less negative the conductivities of electric valves I1, I8 and I9 will be correspondingly increased to control the direct current supplied to armature windings 2, 3 and 4 in accordance with the alternating component of current in these windings.

It is understood that the steady state power output of a dynamo-electric machine of the synchronous type is directly proportional to the product of the terminal voltage, the voltage corresponding to the field current and the sine of the electrical displacement angle between these two voltages and is inversely proportional to the synchronous reactance of the machine. This general statement represents the power of the machine neglecting the double frequency component of power due to the difference in the reactanee in the direct and quadrature axes of the machine. However, for general purposes the above relationship defines the power with sufiicient accuracy. Since the maximum power output of the machine occurs when the derivative of the power with respect to the displacement angle is zero, the maximum power output is obtainable when the displacement angle is slightly less than ninety electrical degrees.

The arrangement of Fig. 2 is similar to that of Fig. 1 and corresponding elements have been assigned like reference numerals. In this figure there is disclosed another embodiment of my invention in which direct current is supplied to the armature windings by means of electric valves 38, 39 and 40, preferably of the type employing an ionizable medium such as a gas or a vapor, and which are associated with controlling means such as saturable reactors 4|, 42 and 43 for controlling the impedance of the respective anodecathode circuitsof these valves. Each of the saturable reactors 4|, 42 and 43 may include a winding 44 connected in series with the associated electric valve and a control winding 45 which controls the impedance of the series winding 44.

' An electric valve circuit 46 including electric valves 4'! and 48, which may be energized from any suitable source of alternating current, is employed to supply direct current to control windings 45 of saturable reactances 4|, 42 and 43 in accordance with the current of the alternating current circuit 1, or in accordance with the current of armature windings 2, 3 and 4 of machine In the particular arrangement shown in the drawings, the electric valve circuit 46 is shown as being energized from the circuit 1 through a transformer 48, and it is to be understood that the circuit 46 may be energized from any other suitable source of current. Electric valves 41 and 48 are provided with control members 58 which are energized by a control circuit including a transformer 52 which impresses alternating voltages on the control members 58 through current limiting resistances 53. The transformer 52 may be energized through any suitable phase shifting arrangement such as a rotary phase shifter 54.

The operation of the embodiment of my invention diagrammatically shown in Fig. 2 is substantially the same as the operation of the embodiment of my invention shown in Fig. 1. Let it be assumed that machine I is operating as a syn-. chronous generator to transmit energy to the alternating current circuit 1 and let it be assumed that the circuit 5| is adjusted so that the current supplied to control windings 45 of saturable reactors 4|, 42 and 43 by circuit 46 is substantially zero within a predetermined range of current in the alternating current circuit 1. Under these conditions, the impedance of the series windings 44 of saturable reactors 4|, 42 and 43 will be relatively large so that there will be practically no unidirectional current in the armature windings 2, 3 and 4 of machine I. As the current of the circuit 1 or as the current of the machine l increases to a value beyond this range of values, the voltage provided by resistance 38 of circuit 21 will be increased to eflect a reduction in the negative potential acting in circuit 5| to increase the conductivities of electric valves 41 and 48, causing these valves to supply current to control windings 45 of the saturable reactors 4|, 42 and 43. As a result, the impedance of the series windings 44 will be decreased thereby permitting the electric valves. 36, 39 and 40' to supply a relatively large component of direct current to the armature windings of machine I, causing the machine to operate higher up on the saturation curve and producing thereby an increase in the steady state power limit of machine I. It is to be understood that the excitation circuit, II will under all conditions respond to control the energization of the field winding 6 to maintain the terminal voltage 01 machine substantially cons ant.

Referring now to Fig. 3 of the accompanying drawings, there is diagrammatically represented another embodiment of my invention for efiecting control of the steady state power limit of dynamo-electric machine in which a circuit controlling means is interposed between the electric valve means and the armature windings of the machine selectively to open and close the electric valve circuit. Various elements in the arrangement shown in Fig. 3 correspond to elements shown in Figs. 1 and 2 have been assigned like reference numerals.

In order to efiect selective control of the unidirectional component of current in the armature windings 2, 3 and 4 of machine I, I employ a suitable circuit controlling means such as a circuit interrupter 55 including a movable contact member 56 biased to the open circuit position, stationary contacts 51, a closing coil 58 and a tripping coil 59. A suitable unidirectional conducing device such as a contact rectifier 68 may be connected in parallel with the closing coil 58 to assure that the closing coil of circuit interrupter 55 is energized with only current of a predetermined polarity. In order to effect energization of the closing coil 58 to establish a unidirectional component of current in the armature windings 2, 3 and 4 when the current of the alternating current circuit 1 increases beyond a predetermined value, I employ a circuit 6| in cluding a controlled electric valve 62 preferably of the type employing an ionizable medium and having a control member 63 which is energized in accordance with the difierence in the voltage provided by the battery 36 and the circuit 21. A current limiting resistance 64 may be connected in series relation with .the control member '63 of electric valve 62. A relay 65 having an actuating coil 66 and an armature member 61 is connected in series relation with the trip coil 59 of the circuit interrupter 55 to prevent energization of the trip coil so long as the electric valve 63 is conductive. The electric valve 62 may be energized from any suitable source of alternating current, such as the circuit 1, through a trans former 68. A resistance 69 is connected in series relation with the electric valve 62 to provide a voltage sufiicient to raise arm 61 when electric valve 62 is conductive.

The operation of the arrangement of my invention shown in Fig. 3 will be considered when the machine is operating as a synchronous generator to supply current to the circuit 1. The excitation system II will operate to control the energization of the field winding 6 so that the terminal voltage of machine is maintained at a substantially constant value. Let it be assumed that the circuit 21 is adjusted to provide a voltage such that the unidirectional negative biasing potential provided by the battery 36 predominates to impress a negative potential on the control member 63 of electric valve 62 to maintain the electric valve 62 nonconductive within a predetermined range of current of the'circuit 1. Under these conditions the circuit interrupter 55 will be maintained in the open circuit position so that no direct current is supplied to the armature windings 2, 3 and 4 of machine If the current of the circuit I increases beyond a predetermined value or, in other words, if alternating current supplied by armature windings 2, 3 and 4 of machine I increases by a predetermined value, the positive voltage provided 7 by resistance 38 will predominate, impressing on control member 83 of electric valve 82 a positive voltage to render electric valve 62 conductive. The voltage appearing across the terminals of resistance 88 will be sufficient to raise the armature member 81 of relay 65 to interrupt the circuit for the tripping coil 58 and the current supplied by circuit 8| will energize the closing coil 58 of circuit interrupter 55 to connect electric valves 38, 33 and 48 to the neutral connection 5 of the armature windings of machine I. As a result thereof, a unidirectional component of current of a predetermined magnitude established by the design of the associated circuit will be established in armature windings 2, 3 and 4 to cause the machine to operate higher up on the saturation curve. If the ,current of the circuit 1 or of the armature winding of machine I decreases below the predetermined value, the negative biasing potential provided by battery 38 will predominate over the positive voltage provided by resistance 38 to render electric valve 62 nonconductive, thereby effecting deenergization of the closing coil 58 and closing relay to trip circuit interrupter 55 by energizing the trip coil 59. In this manner the system operates selectively to open and close the circuit including electric valves 38, 33 and 48 to control the steady state power limit of the machine in accordance with the current in circuit I or in accordance with the current in the armature windings.

Referring now to 4 of the accompanying drawings, there is diagrammatically shown another embodiment of my invention for controlling the steady state power limit of a dynamo-electric machine of the synchronous type. One group of electric valve means comprising electric valves 18, II and I2 is connected across the terminals of the armature windings 2, 3 and 4 and to one terminal of the field winding 8. The other terminal of the field winding 8 is connected to the electrical neutral connection 5 of the armature windings. Each of the electric valves 18, II and I2 is provided with a control member 13 for controlling the conductivity of the associated discharge path and electric valves I8, II and I2 are preferably of the type employing an ionizable medium such as a gas or a vapor. In order to provide a'system of voltages electrical degrees out of phase with the terminal voltages of armature windings 2, 3 and 4, I provide an inductive network 14 comprising windings I5, which are connected to the terminals of armature windings 2, 3 and 4, and a plurality of windings I8 having output terminals which are connected to a second group of electric valves 11, I8 and IS. The inductive network I4 is also provided with a neutral terminal I6 which is connected to the neutral connection 5 of armature windings 2, 3 and 4. The electric valves l1, l8 and II! are also preferably of the type employing an ionizable medium such as a gas or a vapor and each includes a control member 88 for controlling th conductivity of the associated discharge path. The cathodes of electric valves TI, I8 and I8 are connected to the cathodes of electric valves I8, II and I2.

I provide a control circuit 8I for impressing on the control members 13 of electric valves I8, II and I2 and control members 88 of electric valves I1, 18 and I9 alternating voltages variable in phase to maintain the voltage of armature windings 2, 3 and 4 at a substantially constant value and for controlling the electric valves to supply direct current to thearmature windings when the load of the machine I increases beyond a predetermined value. The control circuit 8| comprises a plurality of inductive devices 82, 83 and 84, each of which includes a core member arranged to provide two control voltages. Inductive device 82 is associated with electric valves [8 and I1; inductive device 83 is associated with electric valves 'II and I8, and inductive device 84 is associated with electric valves "and 18. Inductive devices 82, 83 and 84 are provided with exciting windings 85, 86 and8l,respectively, which are energized each in accordance with the voltage of one phase of the three phase alternating current circuit. This source of alternating current may be derived from any suitable source and in the arrangement shown in the drawings is obtained from the alternating current circuit I through any conventional phase shifting arrangement such as the rotary phase shifting device 88. The inductive devices 82, 83 and 84 are also provided with unidirectional biasing windings 88, 98; SI, 92; 33, 84, respectively. These windings serve to impress on the associated core members unidirectional magnetomotive forces of substantially constant value. The inductive devices 82, 83 and 84 are also provided with unidirectional biasing windings 95, 38; 81, 98; 39, I88, respectively. The latter mentioned windings are arranged on the respective core members of inductive devices 82, 83 and 84 to oppose the effect of the unidirectional magnetic biasing windings 88-84, inclusive. Control windings I8I, I82; I83, I84; I85, I88 are associated with inductive devices 82, 83 and 84 respectively, to provide alternating voltages variable in phase to control the conductivities of the associated electric valve means. Current limiting resistances I81 may be connected in series relation with the associated control members. Unidirectional conducting devices I88 are connected across the control windings associated with each of the inductive devices 82, 83 and 84 to short circuit the control winding which is pro-- viding a negative voltage in order to assure that the winding producing a positive voltage is interlinked with a suflicient flux to provide the desired positive voltage. If desired, the core members of inductive devices 82, 83 and 84 may be arranged so that the voltages induced in the control windings are of a peaked wave form.

A voltage sensitive circuit I88 is provided and comprises a transformer II8 having primary windings III connected to the terminals of the armature windings 2, 3 and 4 and having a plurality of secondary windings H2. A rectifier comprising a plurality of electric valves I I3 serves to provide a source of unidirectional voltage II4 the magnitude of which varies in accordance with the voltage of armature windings 2, 3 and 4. A smoothing inductance II5 may be connected in series relation with the associated secondary windings H2 and the electric valves H3 and a capacitance H6 is connected across the output circuit of the rectifier. In order to provide a substantially constant unidirectional voltage, I provide a serially connected glow discharge valve Ill and resistance II8 which are connected in parallel with the capacitance H8. The voltage appearing across the glow discharge valve III supplies a control current of substantially constant magnitude to biasing windings 83-94 of inductivedevices 82, 83 and 84 and also serves to impress a negative unidirectional biasing potential of substantially constant value on control members I3 of electric valves I8, II and 12 75 and on control members 88 of electric valves 11, I8 and I9 through a circuit including a conductor II9, a conductor I 28 and the associated control windings. 'A voltage divider including a resistance I2I having an adjustable contact I22 is ,connected in parallel with the serially connected glow discharge valve III and resistance H8 and serves to provide an adjustable voltage which varies in accordance with the voltage of the armature windings of the machine I to energize biasing windings 95, 91 and 99 of inductive devices 82, 83 and 84, respectively, to control the conductivities of electric valvesI8, II and I2 in accordance with the voltage of the armature windings. A resistance I23 may be connected in series relation with the adjustable contact I22 of the voltage divider and biasing windings 95, 91 and 99.

I provide a current or load responsive circuit I24 including a plurality of current responsive devices such as current transformers 28 and associated rectifiers I 25 for providing a unidirectional voltage, the magnitude of which varies in accordance with the current of the three phases of the alternating current circuit I, or in'accordance with the current of the three phases of the armature windings of machine I. A smoothing reactor I26 may be connected in series relation-with the rectifiers I25 and a capacitance I2I may be connected across the output circuit of the rectifiers I 25 to serve as an energy storage device. The positive terminal of capacitance I2I is connected to the movable contact I22 of the voltage divider through a unidirectional conducting device I28 having an anode I29 and a cathode I38. The positive terminal of capacitance I21 is also connected to biasing windings 98, 98 and I88 of inductive devices 82, 83 and 84 to control the energization of these windings in accordance with the current or load of the alternating current circuit I or in accordance with the current or load of the machine I.

Before explaining the general principles of operation of the embodiment of my invention diagrammatically shown in Fig. 4, the operation of the various individual circuits will be explained. Considering the electric valves III, II, I2, 11, I8 and I9, it will be understood by those skilled in the art that when these valves are of the type employing an ionizable medium the control members are efiective to maintain the electric valves nonconductive and that after the valves have been' rendered conductive by impressing on the control members a sufiiciently positive voltage, the electric valves may be rendered nonconductive only by impressing on the associated anodes a potential sufliciently negative relative to that of the cathode for a time equal to or greater than the time of deionization of the valves. The voltages impressed on the control members I3 of electric valves III, II and I2 and control members 88 of electric valves 11, I8 and 19 comprise a unidirectional negative biasing potential of substantially constant value provided by the glow discharge valve III and the alternating voltages oi! peaked wave form provided by control windings I8 II 88, of inductive devices 82, 83. and 84. Considering one of the inductive devices in particular, as for example inductive device 82, it is to be understood that the voltages provided by control windings IIII and I82 are 180 electrical degrees out of phase with respect to each other, and that these voltages tend to render the associated electric valves I8 and 11, respectively, conductive during intervals displaced 180 electrical degrees. Biasing windings 95, 91 and 99 of inductive devices 82,

83 and 84, respectively, are arranged to oppose the magnetomotive forces established by windings 89, 9| and 93 to control the phase oi! the alternating voltages of peaked wave form induced in control windings I M I83 and I85 in accordance with the magnitude of the armature voltage of machine I. Windings- 89-94, inclusive, establish in the respective core members of inductive devices 82, 83 and 84 unidirectional magnetomotive forces tending to advance the phase of the control voltages provided by control windings I8 II86 to the full-on position. Upon increase in armature voltage of machine I,-the incident increase in energization of windings 95, 91 and 99 will efiect a retardation in phase of the voltages induced in control windings I8I, I83 and I85 to decrease the conductivities of electric valves I8, H and I2 and to thereby effect a decrease in the energization of the field winding to return the armature voltage of machine I to the predetermined value to be maintained. In like manner the energization of windings 96, 98 and I88 of inductive devices 82, 83 and 84 will control the phase of the voltages induced in control windings I82, I84 and I88 to control the conductivities of electric valves 11, I8 and I9 within a predetermined range of current or load of the machine I or of the alternating current circuit I.

It is to be understood that the voltage sensitive circuit I89 will provide a unidirectional voltage the magnitude of which varies in accordance with the voltages of the three phases of the armature windings of machine I, or in accordance with the voltage of the alternating current circuit I. By virtue of the characteristics of the glow discharge valve I II, the voltage appearing across its terminals will be substantially constant and by the proper adjustment of the movable contact I22 of the voltage divider there is provided means to obtain a component of voltage of the output circuit I I4 which varies in accordance with the voltage of machine I.

Within a predetermined range of current supplied by the machine I to the alternating current circuit I, the electric valves I8, II, I2, 11, I8 and I9 will be controlled to operate as a six-phase rectifier to supply unidirectional current to the field winding 6 to maintain the armature voltage at a substantially constant value, and no unidirectional component will exist in the armature windings 2, 3 and 4 since the current is conducted from the neutral connection 5 of these windings to the neutral terminal 18' of the inductive network I4 through the neutral connection. How ever, as the current supplied to the alternating current circuit 1 increases beyond a predetermined value, the voltage supplied by the circuit I24 increases to a value sufiiciently great to render the cathode I38 of electric valve I28 positive relative to the anode I29, so that beyond this value of current the energization of windings 98, 98 and I88 of inductive devices 82, 83 and 84 is increased to retard in phase the control voltages of windings I 82, I84 and I86 to render electric valves 11, I8 and I9 conductive for progressively smaller intervals during each cycle. Within this range of current transfer where the voltage impressed on control members 88 of electric valves 11, I8 and I9 is progressively retarded in phase, it is to be understood that the rateat which the saturation of the core member is accomplished relative to the current of the armature windings may be controlled by adjustment of the movable contact I22 of the voltage divider and by the adjustment of other features of the control circuit 8|. At a second predetermined valueof current transfer abovethe first value, it will be understood that by virtue of the increase in voltage of capacitance I21 and incident energization of windings 96, 98 and I 00, the voltages impressed on control members 80 of electric valves 'II, I8 and I9 will be retarded 'sufiiciently to maintain these electric valves nonconductive so that the electric valves III, II and I2 operate as a three phase half wave rectifier. For values of current above the second predetermined value, electric valves 11, 18 and 19 are controlled predominantly in accordance with the current. Under this condition of operation, an appreciable direct current is conducted through armature windings 2, 3 and 4 to cause said machine to operate higher up on the saturation curve and to increase the steady state power limit of machine I.

The simplified diagram 01' Fig. 4a will be of assistance in explaining the general principles of operation of the embodiment shown in Fig. 4. The elements of the circuit of Figs. 4a have been assigned reference numerals corresponding to the respective elements of Fig. 4. Within a predetermined range of current transfer, the system will respond to control the energization of the field winding 6 in accordance with the armature voltage of machine I or in accordance with the voltage of the alternating current circuit I since control windings 95-400, inclusive, are connected to be energized in accordance with a unidirectional voltage which varies in accordance with the voltage to be regulated, that is, connected to be energized in accordance with a predetermined component of the voltage appearing across resistance I 2| of the voltage divider. So longas the current transmitted does not exceed a predetermined value to increase the voltage of capacitance I21 too greatly, the voltage provided by resistance I2I through movable contact I22 will control the energization of windings 9B, 98 and Ilili of inductive devices 82, 83 and 84 in accordance with the voltage of the circuit. In other words, the electric valves 11, 18 and 19 as well as electric valves 10, H and 12 will be controlled in accordance with the armature voltage of machine I. However, as the current transmitted exceeds the predetermined range of values, the voltage impressed on control members 80 of electric valves 11, I8 and 19 will be retarded in phase to decrease the conductivities of these valves. During this state of operation, the voltage of the machine I will be maintained at a constant value by virtue of the control of electric valves 10, H and 12 through windings 95, 9'! and 99 of inductive devices 82, 83 and 84. As the current transmitted obtains a second predetermined value above the range of values, the windings 96, 98 and I will be energized to retard in phase the voltages impressed on control members 80 of electric valves 11, I8 and 19 so that these valves are maintained nonconductive. Under this condition of operation the electric valves 10, II and '12 control the energization of the field winding 6 of machine I to maintain the armature voltage thereof at a sub stantially constant value and since these valves are operating as a half wave rectifier, the unidirectional component of current conducted through windings 2, 3 and 4 will cause the machine to operate higher upon the saturation curve, efiecting thereby a material increase in the steady state power limit of the machine.

While I have shown and described my invention as applied to a particular system of connections and as embodying various devices diagrambetween said alternating current circuit and said direct current circuit for supplying current thereto and each of said electric valve means being provided with a control member for controlling the conductivity thereof, a second group of electric valve means interposedbetween said alternating current circuit and said direct current circuit for supplying current to said direct current circuit and each of said valve means being provided with a control member for controlling the conductivity thereof, and a control circuit for energizing said control members comprising means for impressing on said control members alternating voltages variable in phase to control the conductivity of said valve means in accordance with the voltage of said alternating current circuit within a predetermined range of current of said alternating current circuit and for progressively retarding in phase the voltages impressed on the control members of said second group to decrease the conductivity thereof and for progressively advancing in phase the control voltages impressed on the control members of said first mentioned group of electric valves for values of current of said alternating current circuit above said predetermined range.

2. In combination, an alternating current circuit interconnecting an alternating current source and an alternating current load, a direct current circuit, two groups of electric valve means connected between said alternating current circuit and said direct current circuit for transmitting energy therebetween and each electric valve means being provided with a control member for controlling the conductivity thereof, a control circuit for impressing on said control members alternating voltages variable in phase in accordance with a predetermined electrical condition of 'said alternating current circuit, means for controlling the phase of said alternating voltages relative to the voltage of said alternating current circuit to control both groups of said electric valve means in accordance with said electrical condition within a predetermined range of a second electrical condition of said alternating current circuit, and means for controlling one of said groups of electric valve means predominately in accordance with said second electrical condition when said second electrical condition exceeds said predetermined range.

3. In combination, an alternating current circuit interconnecting an alternating current source and an alternating current load, a direct current circuit, two groups or" electric valve means interconnecting said circuits for transmitting energy therebetween and each electric valve means having a control member for controlling the conductivity thereof, a control circuit for impressing on said control members alternating voltages variable in phase relative to the voltage-oi said alternating current circuit, a voltage sensitive circuit for controlling the phase of said alternat ing voltages in accordance with the voltage of said alternating current circuit within a predetermined range of current of said alternating current circuit, and a current responsive circuit for controlling the phase of the alternating control voltages impressed on the control members of one of said groups of electric valve means predominately in accordance with the current of said alternating current circuit for values of' current above said predetermined range of values.

4. In combination, a polyphase alternating current circuit interconnecting an alternating current source and an alternating current load, a direct current circuit, a plurality of electric valve means each having a control member for controlling the conductivity thereof, a control circuit for energizing said control members comprising a plurality of inductive devices each including a core member,- an exciting winding, a pair of opposing unidirectional magnetic biasing windings and a control winding for furnishing an alternating voltage variable in phase relative to the voltage of said exciting winding, and a voltage sensitive circuit including a rectifier for providing a unidirectional voltage variable in accordance with the voltage of said alternating current circuit, a voltage divider connected across the output circuit of said rectifier and a seriallyconnected resistance and a glow discharge valve connected in parallel with said voltage divider, one of said unidirectional biasing windings of each of said devices being connected to be energized in accordance with the voltage appearing across said glow discharge valve to establish in said core member a unidirectional magnetic flux of constant magnitude and the other of said unidirectional biasing windings of each of said devices being energized in accordance with a component of voltage of said divider to control the phase of the alternating voltage provided by the associated control winding.

5. In combination, an alternating current circuit interconnecting an alternating current source and an alternating current load, a second circuit, two groups of electric valves interconnecting said circuits for transmitting energy therebetween and each electric valve means having a control member for controlling the conductivity thereof, a control circuit for impressing on said control members control voltages, a voltage sensitive circuit for providing a unidirectionallvoltage which varies in accordance with the voltage of said alternating current circuit to control said control voltages,-a current responsive circuit for providing a unidirectional voltage which varies in accordance with the current or said alternating current circuit, and means interposed between said voltage sensitive circuit and said current responsive circuit for controlling the control voltages impressed on the control members oi! one oi'said groups of electric valves in accordance with the difference of said unidirectional voltages.

6. In combination, an alternating current cir-s cuit interconnecting an alternating current source and an alternating current load, a second circuit, two groups of electric valve means in-' terconnecting said circuits for transmitting energy therebetween andeach electric valve means having a control member for controlling the con-- ductivity thereof, a control circuit for impressing on said control members alternating voltages variablein phase relative to the'voltage 01 said alternating current circuit, a voltage sensitive circuit for providing a unidirectional voltage which varies in accordance with the voltage of said alternating current circuit to control the phase of the alternating control voltages, a current responsive circuit for providing a unidirectional voltage which varies in accordance with the current of said alternating current circuit, and means interposed between said voltage sensitive circuit and said current responsive circuit for controlling the phase of the control voltages impressed on the control members of one of said groups of electric valves in accordance with the difference of said unidirectional voltages.

7. In combination, an alternating current circuit interconnecting an alternating current source and an alternating current load, a direct current circuit, two groups of electric valve means interconnecting said circuits for transmitting energy therebetween and each electric valve means having a control member for controlling the conductivity thereof, a control circuit comprising a plurality of inductive devices each having a core member, an exciting winding, a pair of unidirectional biasing windings and a control winding for providing an alternating voltage variable in phase for energizing the control member of one of said electric valve means, a voltage sensitive circuit for providing a unidirectional voltage variable in accordance with the voltage of said alternating current circuit and including a glow discharge valve for providing a substantially constant source of unidirectional voltage for energizing one of said biasing windings of each oi said inductive devices and a voltage divider for energizing the other biasing winding of the inductive devices associated with one of said groups of electric valve means in accordance with the voltage of said alternating .current circuit, a current responsive circuit for providing a unidirectional voltage which varies in accordance with the current of said alternating current circuit, and means interposed between said voltage divider and said current responsive circuit for energizing the other biasing,windings of the inductive devices associated with the other group of said electric valve means in accordance with the difierence between said unidirectional voltages.

8. In combination, an alternating current circuit interconnecting an alternating current source and an alternating current load, a direct current circuit, two groups of electric valve means connected between said alternating current cir cuit and said direct current circuit for transmitting energy therebetween andeach electric valve means being provided with a control member for controlling the conductivities thereof, and an excitation system for impressing on the control members control voltages variable in accordance with a predetermined electrical condition of said alternating current circuit, means for controlling said voltages to control both groups of electric valve means in accordance with said electrical condition within a predetermined range of a second electrical condition of said alternating current circuit and means for controlling one of said groups of electric valve means predominately in accordance with said second electrical condition when said second electrical condition exceeds said predetermined range.

EIMO E. 'MOYER. 

